In mastocytosis the number of mast cells is increased, and the most common manifestation is urticaria pigmentosa. We describe four children, of which two developed ulceration of the upper gastrointestinal tract. Main symptoms in the other children were vomiting, heartburn and abdominal pains, which were manifested as intense crying spells. The symptoms are caused by mediators such as histamine being released from the mast cells, and blockers of the histamine receptor thus play a central role in their treatment. The childrens' condition was significantly alleviated by adequate medication: the ulceration healed, symptoms were relieved and growth was normalized.